Current concepts on the pathogenesis and markers of preterm births

Increased rate of prematurity associated with antenatal antiretroviral therapy in a German/Austrian cohort of HIV-1-infected women

OBJECTIVE

The aim of the study was to assess the risk of adverse pregnancy outcomes after antenatal antiretroviral therapy in a well-defined prospective cohort of nontransmitting HIV-infected women.

METHODS

Prospective monitoring of 183 mother-child pairs from 13 centres in Germany and Austria, delivering between 1995 and 2001, was carried out. Following German-Austrian guidelines recommending an elective Caesarean section (CS) at 36 weeks, prematurity was defined as <36 weeks' gestation for these analyses.

RESULTS

Of 183 mother-child pairs, 42% were exposed to antenatal monotherapy and 17% to dual therapy. Of the 75 women exposed to highly active antiretroviral therapy (HAART), 21 (28%) received protease inhibitor (PI)-based HAART and the remaining 54 received nonnucleoside reverse transcriptase inhibitor-based HAART. In multivariable analysis (176 pregnancies), PI-based HAART exposure during pregnancy was associated with an increased risk of premature delivery [adjusted odds ratio 3.40; 95% confidence interval (CI) 1.13-10.2; P=0.029, compared with monotherapy]. Congenital abnormalities affected 3.3% infants. Perinatally, 18.9% of children (34 of 179) had respiratory problems requiring interventions, which were associated with prematurity but not with type of treatment exposure. From adjusted regression analysis, the mean birth weight z-score for children exposed to HAART with PI (+0.46; 95% CI 0.01-0.92; P=0.047) or dual therapy (+0.43; 95% CI 0.03-0.82; P=0.034) was slightly but significantly higher than that for those exposed to monotherapy; head circumference was appropriate for gestational age and there were no significant differences between treatment groups.

CONCLUSIONS

Use of antenatal PI-based HAART initiated before or during pregnancy was associated with a significantly increased risk of premature delivery at <36 weeks' gestation. The overall crude prematurity rate was 34% (63 of 183; 95% CI 28-42).

Genetics of preterm labour

The identification of women at risk of preterm labour remains an important challenge. While current prevention programmes rely on overt clinical and environmental parameters, the clustering of preterm labour within families and recurrence in susceptible women presents the case for a complex underlying genetic predisposition. Genetic polymorphisms are useful markers to identify high risk groups, although they provide little information either to their underlying functionality or the pathophysiological mechanisms involved; these must be validated through complementary analytical approaches. Data interpretation and inter-study comparisons must be made with caution, taking into account population size, study power, racial differences, inclusion/exclusion criteria and any underlying gene-environment and feto-maternal interactions. Large-scale, multicentre genetic studies coupled with high-throughput screening techniques are the most viable approaches to identify multilocus preterm labour susceptibility screening panels. Preventive strategies may then be applied to those women most likely to benefit from intervention.

Maternal infection and white matter toxicity

Studies examining maternal infection as a risk factor for neurological disorders in the offspring have suggested that altered maternal immune status during pregnancy can be considered as an adverse event in prenatal development. Infection occurring in the mother during the gestational period has been implicated in multiple neurological effects. The current manuscript will consider the issue of immune/inflammatory conditions during prenatal development where adverse outcomes have been linked to maternal systemic infection. The discussions will focus primary on white matter and oligodendrocytes as they have been identified as target processes. This white matter damage occurs in very early preterm infants and in various other human diseases currently being examined for a linkage to maternal or early developmental immune status. The intent is to draw attention to the impact of altered immune status during pregnancy on the offspring for the consideration of such contributing factors to the general assessment of developmental neurotoxicology.

Fetal growth rates and the very preterm delivery of twins

OBJECTIVE

Our objective was to determine whether slow fetal growth rates and twin growth patterns from 20 weeks' gestation to delivery are associated with very preterm delivery.

STUDY DESIGN

Available charts were reviewed for twin pregnancies, delivered between 1979 and 2002, at 4 U.S. medical centers. The sample of 1612 pregnancies delivered at 28 week's gestation or greater and had at least 2 ultrasound evaluations of fetal size from 20 to 28 weeks or from 28 weeks to delivery for estimation of fetal growth rates (grams per week). Slow fetal growth (below the 10th percentile) was defined as less than 90 grams per week at 20-28 weeks and 168 g/week from 28 weeks to delivery. The main outcome measure was the timing of delivery.

RESULTS

Of the women delivering twins, 5.3% delivered extremely preterm (28-30 weeks), 8.5% very preterm (31-32 weeks), and 40.1% preterm (33-36 weeks). Patterns of growth for the pair were highly associated with very preterm delivery. Compared with neither growing slowly (1.7%), 4.9% delivered very preterm if only 1 twin grew slowly. Very preterm was 14.6% (adjusted odds ratio 9.81; 95% confidence interval, 3.50-27.48) with both growing slowly from 28 weeks on and 20.0% (adjusted odds ratio 15.04; 95% confidence interval 5.13-44.11) with both growing slowly over both intervals. Survival analyses indicated that twins with normal growth in both intervals remained undelivered for a significantly longer number of days (P < .0001) than pairs in which one or both twins were growing slowly.

CONCLUSION

Very preterm delivery of twins seems to be preceded by slowed or compromised fetal growth for the pair.

Explaining disproportionately high rates of adverse birth outcomes among African Americans: the impact of stress, racism, and related factors in pregnancy

Compared with European Americans, African American infants experience disproportionately high rates of low birth weight and preterm delivery and are more than twice as likely to die during their 1st year of life. The authors examine 5 explanations for these differences in rates of adverse birth outcomes: (a) ethnic differences in health behaviors and socioeconomic status; (b) higher levels of stress in African American women; (c) greater susceptibility to stress in African Americans; (d) the impact of racism acting either as a contributor to stress or as a factor that exacerbates stress effects; and (e) ethnic differences in stress-related neuroendocrine, vascular, and immunological processes. The review of literature indicates that each explanation has some merit, although none is sufficient to explain ethnic disparities in adverse birth outcomes. There is a lack of studies examining the impact of such factors jointly and interactively. Recommendations and cautions for future research are offered.

Infection-related morbidities in the mother, fetus and neonate

Only partially understood host defense mechanisms operate against infections affecting maternal and fetal morbidity. Subclinical ascending infections through the lower female genital tract are predominant worldwide. Important micronutrient deficiencies may prevail in low-income countries where these infections are much more common than in high-income countries. Important morbidities related to poor perinatal outcome both for the mother and for the fetus and newborn comprise preterm birth, prelabor rupture of membranes, placental abruption (predelivery detachment of the placenta), postpartum sepsis and maternal anemia. In the fetus, sepsis and intrauterine growth retardation are suspected to be consequences of ascending maternal infections. In the newborn, septicemia and respiratory disorders as well as some neurological disorders seem to be consequences of such ascending genital infections in the pregnant woman. It is concluded that much more attention should be given to efforts to elucidate the host defense mechanisms and antimicrobial barriers from the vagina through the cervix, fetal membranes and amniotic fluid including the early fetal immunocompetence in the second and the third trimester of pregnancy.

A perspective on the diagnosis of preterm labor

Over the past few decades there has not been any significant reduction in the rate of preterm birth. As we enter into a new millennium, prematurity is still the leading cause of perinatal morbidity and mortality in the non-anomalous infant. The only major contributions in reducing perinatal mortality in the preterm infant are those in the field of neonatology, while the area of preterm birth prevention has lagged far behind. This article highlights the research and clinical challenges that stand in the way of making a timely yet accurate diagnosis of preterm labor. In addition, possible pathways in the evolution of preterm labor are discussed with emphasis on their significance to diagnosis and treatment.

Elevated amniotic fluid ferritin levels are associated with inflammation-related pregnancy loss following mid-trimester amniocentesis

OBJECTIVE

Occult infection accounts for up to 12% of pregnancy losses following genetic amniocentesis. Elevated serum and cervical fluid levels of ferritin, an acute-phase reactant, have been associated with spontaneous preterm delivery. We determined the association between amniotic fluid (AF) ferritin levels and post-amniocentesis pregnancy loss.

METHODS

We performed a case-control study involving 66 women with a non-anomalous fetus who had a spontaneous pregnancy loss within 30 days following genetic amniocentesis and 66 term controls matched for maternal age, gestational age, time of test and indication for amniocentesis. Amniotic fluid ferritin and interleukin-6 (IL-6) levels were measured using commercially available kits.

RESULTS

Mean (+/- SD) AF ferritin levels were similar between the cases (19.3 +/- 21.4 ng/ml) and the controls (19.8 +/- 22.7ng/ml) (p = 0.9). Mean (+/- SD) AF IL-6 levels were significantly higher in the women with post-amniocentesis pregnancy loss (4.0 +/- 13.1 ng/ml) than in controls (0.5 +/- 0.7 ng/ml) (p = 0.04). A significant proportion (12.1%, 8/66) of the women with post-amniocentesis pregnancy loss had elevated amniotic fluid IL-6 levels (> 3 SD, 2.5 ng/ml) indicating inflammation, as compared to none in the control group (p = 0.01). In this subgroup of women with pregnancy loss and elevated IL-6 levels, AF ferritin levels were significantly elevated (52.0 +/- 45.5 ng/ml) compared to the level in women who had a term delivery (19.8 +/- 22.7 ng/ml) (p = 0.002), and were strongly correlated with IL-6 levels among the cases (r = 0.67, p < 0.001).

CONCLUSION

The strong correlation of AF ferritin with IL-6 levels, along with the high ferritin values in cases with high AF IL-6, indicates that ferritin is a marker of inflammation in asymptomatic women destined to have an early pregnancy loss.

Socioeconomic status and preterm birth: New Zealand trends, 1980 to 1999

BACKGROUND

While a number of countries have reported rising preterm birth rates over the past two decades, none has examined the effects of socioeconomic status on preterm birth at a national level.

AIM

To document the changing incidence of preterm birth in New Zealand over the past 20 years and to determine whether particular socioeconomic or ethnic subsections of the population have contributed disproportionately to the changes seen.

METHODS

Birth registration data routinely available from the New Zealand Health Information Service were analysed for the period 1980-99. Information for a total of 1 079 478 singleton live births was linked by Domicile Code to the New Zealand Deprivation Index, a small area index of deprivation.

RESULTS

Singleton preterm birth rates rose by 37.2% during the 20 year period, from 4.3% in 1980 to 5.9% in 1999. Rates increased by 71.9% among those living in the most affluent areas, but by only 3.5% among those living in the most deprived areas, resulting in the disappearance of a socioeconomic gradient in preterm birth that had existed during the early 1980s.

CONCLUSIONS

This study challenges traditional thinking on the associations between socioeconomic status and preterm birth. Further research is necessary if the changes that have occurred in New Zealand over the past 20 years are to be fully understood.

Cerebral white matter damage in the preterm infant: pathophysiology and risk factors

Based on clinical, epidemiologic, and experimental studies, the aetiology of white matter damage, specifically periventricular leukomalacia (PVL), is multifactorial and involves pre- and perinatal factors possibly including genetic factors, hypoxic-ischaemic insults, infection, excess cytokines, free radical production, increased excitatory amino acid release, and trophic factor deficiencies. The article summarizes research findings about the aetiology of white matter damage and cerebral palsy in preterm infants. The information is organized according to specific antecedents, for which we present epidemiological and neurobiological data. The most important prenatal factor appears to be intrauterine infection. We discuss the evidence supporting the hypothesis that the foetal inflammatory response contributes to neonatal brain injury and later developmental disability. We recently established an animal model of excitotoxic lesions in the developing mouse brain. Brain damage was induced by intra-cortical injections of ibotenate, a glutamatergic agonist. When administered on post-natal day 5 ibotenate induced the formation of white matter cysts. Our animal model could be used to further explore the mechanisms involved in the formation of PVL. Potentially preventive strategies will be discussed.